export function shuffle(arr) {
  let _arr = arr.slice()
  for (let i = _arr.length - 1; i >= 0; i--) {
    let j = Math.floor(Math.random() * (i + 1))
    let t = _arr[i]
    _arr[i] = _arr[j]
    _arr[j] = t
  }
  return _arr
}
